Therefore, only the low-temperature oxide phases, Fe 3 0 4 and Fe 2 0 3, are commonly observed in steam-grown scales from operating boilers. Magnetite is the predominant phase; haematite occurs at the oxide-steam interface, but only as a thin and discontinuous oxidation layer (4).
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What is magnetite layer in boiler? Magnetite is an iron oxide, [Fe3O4]. It deposits in the form of thin layer on boiler steel surface and passivates the surface and thus protects the...
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Figure 11: Heat distribution in a boiler tube with an 80 µm magnetite and a 20 µm hematite layer and a close-up of heat distribution in the layers. Figure 12: Heat distribution in a boiler tube with a 450 µm wustite, magnetite and a 10 µm hematite layer and a close-up of the heat distribution in the layers.
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Creep tests have also been performed on as-received and welded specimens of modified 9Cr-1Mo steel, in the temperature range of 500–700°C and stress range of 50–200 MPa. Microstructural ...
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This can be easily seen, as this magnetite is a black layer on the metallic surface. This phenomenon of magnetite forming in water or steam pipes, is know from water systems having an oxygen-deficient. In other words, if there is not enough oxygen in the water to finalize the oxidation, then magnetite (Fe3O4) forms, instead of the more common ...
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The oxide layer formed on the internal surface of low alloy steel tubes (up to 3% Cr) exposed to the steam gen- erated in boilers consists of a layer with different levels. When the metal temperature is below 560°C and there is a high partial pressure of oxygen, a À lm consisting of magne- tite (Fe 3 O 4 ) and other of hematite (Fe 2 O 3 ...
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The simplified reaction is given as follows 3 Fe(s) + 4 H 2 O(l) → Fe 3 O 4 (s) + 4 H 2 (g) Magnetite forms a dark, passive and protective layer on the boiler tube surface, limiting further corrosion. Corrosion product transport in feed water piping can lead to magnetite particles being transported downstream where, under certain conditions ...
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The outer magnetite layer is Fe 3 O 4 and grows out from the original metal surface. The inner magnetite layer is (Fe, Cr) 3 O 4 and grows inward from the original metal surface. The interface between the two magnetite layers corresponds to the original metal interface (Cory and Herrington, 1987). Wüstite (FeO) may form under the magnetite layer.
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Caustic gouging of boiler tubes used in fossil fuel-fired electric power plants constitutes an important corrosion problem. Under proper boiler operating conditions, the internal surface of boiler tubes is protected from corrosion by a thin film of magnetite (Fe 3 O 4) which is a black, dense, well crystallized (unhydrated), and highly insoluble iron oxide.
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One deposit that has long been used as a laboratory to address the controls on layer formation in layered intrusions is the Main Magnetite Layer (MML) in the Upper Zone of the Rustenburg Layered ...
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Within the boiler itself, the biggest problems caused by scale is overheating leading to the rupture of boiler tubes. While the thin dense film of Magnetite is thermally conductive, thicker porous layers create a more ceramic-like insulating layer which limits the thermal transfer. It is …
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A simple galvanic sensor was developed to determine the onset of iron corrosion under conditions similar to those used for removing the iron oxide (magnetite) layer from steam boilers with a hy-drochloric acid solution. Since the potentials of magnetite and iron are different, the initiation of the dissolution of the magnetite layer …
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Mechanical performance of magnetite protective layers on boiler components within the temperature range up to 320/sup 0/C (Journal Article) | ETDEWEB. You need JavaScript …
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It can be seen that some protective magnetite layers were broken down on the inner surface on the water side (Fig. 6d). It was reported that the extremely porous magnetite film, marked with a red dot circle, is often found in boilers, and it was generated by dissolution of magnetite film induced by caustic corrosion [ 9 ].
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Magnetite, Fe3O4, is a naturally occurring, safe iron oxide with an unusual and useful combination of properties compared to the better-known functional fillers for plastics. ... Huijbregts WMM, Snel A (1972) The protection effectiveness of magnetite layers in relation to boiler corrosion. In: 5th international congress on metallic corrosion ...
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A statutory inspection of a boiler steam drum that had seen 10 years of service revealed a few scattered cracks on the inner surface of the drum. The drum was used in the refinery and petrochemical industry. ... The drum internal surfaces were in healthy condition with protective magnetite layer that formed during service. …
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PDF. 2 Excerpts. Various ultrasonic (UT) methods, techniques, and transducers, used for internal oxide/magnetite layer detection and its thickness measurement in boiler tubes are described and analyzed. Obtained results (computer simulated and experimental) have demonstrated that using UT waves, it is quite possible to detect and measure even ...
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Boiler water has to be at a pH of 9–10.2 in order to preserve the magnetite layer of steel. Iron oxidation in boilers results in the formation of two magnetite layers. …
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The formation of a healthy magnetite (Fe₃O₄) film on the internal surfaces of boiler tubes is crucial for ensuring their longevity and operational efficiency. This …
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The magnetite produced is black iron oxide. Under normal conditions, this is the typical product of corrosion. However, it is also this reaction that inhibits excessive corrosion in steam boilers. In a new or cleaned boiler, the initial corrosion process produces this magnetite film as a tenacious layer at the steel surface.
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The end result of these reactions is the operational protective oxide film in the form of magnetite, or mixtures of hydrated hematite and magnetite, depending on the operational pressure of the boiler. A pure magnetite film or integral mono-molecular magnetite surface on the boiler steel can be obtained at operational pressures over 30 bar.
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Sludge is formed by substances like MgCl2, MgCO3, MgSO4 and CaCl2. Sludge has greater solubilities in hot water than cold water. Scale. 1) If the precipitate forms hard and adherent coating on the inner walls of the boiler, it is called scale. 2) Scale is formed by substances like Ca (HCO3)2, CaSO4 and Mg (OH) 2. 1.5.2.
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The third step is to maintain this magnetite layer throughout the life of the plant. If the water quality goes down, this protective layer will be destroyed and corrosion starts damaging the tubes. In a 500 MW power thermal …
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As long as the magnetite layers are left undisturbed, their growth rate rapidly diminishes. The second type of iron oxide in a boiler is the corrosion products, which may enter the …
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Boiler water has to be at a pH of 9–10.2 in order to preserve the magnetite layer of steel. Iron oxidation in boilers results in the formation of two magnetite layers. The outer layer is porous, is easily penetrated by water and aggressive ions, and is the site of surface reactions. The inner layer is relatively less porous, and its growth is ...
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If the magnetite layer grows excessively thick over time, it can act as an insulating barrier on the surface of the boiler tubes. This hinders heat transfer from the hot boiler water to the ...
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The chelation of magnetite (the oxide formed under boiler conditions-a mix of Fe2O3 and FeO) is possible because the chelant combines with the ferrous (FeO) portion of the magnetite. Overfeed (high levels) of chelant can remove large quantities of iron oxide. However, this is undesirable because high excess chelant cannot distinguish between ...
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The presence of magnatite in steam systems means that your customers are likely doing their water treatment correctly. You want to build a layer of magnatite in the boiler to protect the steel from corrosion. I have always used a magnet to test polished metals because a magnet won't stick to most stainless steels. You might get more help …
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The economically important Main Magnetite Layer (MML), near the bottom of the Upper Zone, has ~1 –2.5 m thickness and crops out intermittently over hundreds of km of strike extent10 –14,22. It ...
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The formation of a magnetic oxide layer in steam boilers typically involves a process called magnetite (Fe3O4) layer formation. This layer serves as a protective coating on …
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